This invention relates in general to vehicular air-conditioning systems. In particular, this invention is concerned with a refrigeration circuit that uses carbon dioxide as a refrigerant and includes an oil separator.
Air-conditioning systems are provided in vehicles for maintaining interior air at desired temperatures. Conventional vehicular systems include a compressor, a condenser, an expansion valve (or orifice tube), and an evaporator. A refrigerant is repeatedly circulated through the cycle of compressor, condenser, expansion valve, and evaporator to maintain interior air at desired temperatures.
A typical refrigerant cycle operates in the following manner. A refrigerant is first compressed by a compressor to a high temperature and high pressure gas and then directed to a condenser. In the condenser, the gas is changed to a lower temperature, high pressure liquid as it is cooled by a heat exchanger operating with the surrounding atmosphere or cooling water. The high pressure liquid loses pressure and becomes chilled when it passes through an expansion valve. When the low pressure liquid passes through an evaporator, it evaporates as it absorbs ambient heat. The evaporated refrigerant, i.e. a gas, flows into the compressor and the process is repeated.
Oil is mixed with the refrigerant gas for lubricating and cooling the compressor. The refrigerant mixture of gas and oil is circulated inside the compressor. When the gaseous mixture is discharged from the compressor, oil remains suspended in the gas. Unless removed, the oil can travel through the condenser, expansion valve, and evaporator and adversely affect the performance of the system. Oil traveling with the refrigerant displaces refrigerant, and the efficiency of the air conditioning system decreases.
When discharged oil is not returned to the compressor, or when the return time is lengthened, a shortage of oil can occur in the compressor. Such a shortage can adversely affect operation of the compressor.
The present invention includes a vehicular refrigeration circuit using carbon dioxide and an oil separator. The oil separator is positioned directly downstream of the discharged refrigerant mixture exiting a compressor. Separated oil is routed through a capillary tube that throttles and cools the oil. The reduced pressure oil is routed directly back to the compressor to provide lubrication of the compressor and pressure regulation of a crank chamber inside the compressor. While the present invention is particularly adapted for carbon dioxide, CO2, other refrigerants can be used with the system.
In a preferred embodiment, a vehicular air conditioning system includes a compressor having a crank chamber, a suction chamber, and a discharge chamber. A refrigerant mixture includes carbon dioxide and oil. A conduit connects the discharge chamber of the compressor directly with an oil separator to route the refrigerant mixture directly to the oil separator. A capillary tube is connected between the oil separator and the crank chamber of the compressor to cool and throttle oil enroute directly to the crank chamber of the compressor.
Various objects and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the preferred embodiment, when read in light of the accompanying drawings.